Cobalt alloys



United States Patent F COBALT ALLOYS '9 Claims. (Cl. 75--170) 'Ihe instant invention relates to improved cobalt alloys and the methodof making the same. More particularly, it .relatesto .the addition of small amounts of various selected materials to cobalt and cobalt-base alloys whereby' alloys having markedly improved physical and metallurgical properties are obtained. It is well known among cobalt metallurgists that the commercialgrade metal and various alloys produced therefrom are practically impossible to forge. This serious defect arises from the fact that the metal and the alloys are so-called hot short, i.e., they are extremely brittle at elevated temperatures. We have discovered a method whereby such defect may be cured, and it is to such method and the novel compositions resulting therefrom that the instant invention is primarily directed.

Although we are not completely certain of the underlying reason for the hot shortness of commercial cobalt materials, our best evidence points to the fact that the presence of sulfur is the cause. Most likely, in even minute amounts, there is formed a low-melting, brittle cobalt-sulfur eutectic phase which appears along grain boundaries and causes the hot shortness. We, of course, do not wish to be limited to such theory, for it should be evident that no matter what the underlying reasons be, our compositions present a definite improvement in this art. Commencing with such sulfur eutectic theory we reasoned that the addition to the cobalt melt of selected elements which negate the sulfur effects would improve the physical properties of both cobalt per se and cobalt base alloys, and regardless of the validity of the original theory, we have found that the addition of materials selected initially to combine with the sulfur substantially eliminated the hot short defect. Following such theory it was felt that if there is added to the cobalt melt another element which strongly combines with sulfur to form' a comparatively high melting compound, the sulfide phase will appear not at the grain boundaries, but distributed within the grains where its detrimental elfects are only slight. Perhaps this theory is not correct, but the beneficial effects of our additives are substantial, as will be seen below.

In view of the foregoing, a primary object of the instant invention is to provide forgeable cobalt alloys.

Another object of our invention is to provide a method of producing forgeable cobalt alloys.

A further object of our invention is to provide readily forged cobalt alloys from commercial quality cobalt.

Still another object of our invention is to provide cobalt alloys which may be utilized in elevated temperature operations.

Yet another object of our invention is to provide cobalt alloys which are not hot short.

Other objects, features and advantages of the instant invention will become apparent to those skilled in this art from the following detailed disclosure thereof.

We have found that the following additives in small amounts achieve the purposes of our invention: cerium, mischmetal, and niobium. Such materials, either singly 2 ,983,602 Patented May 9, 1961 or in combination, may be added to cobalt or cobalt-base alloys to vastly improve the properties thereof.

In all of our work, the results of which are presented below, a single base material was used, viz., a good grade of commercially pure cobalt rondells. Chemical analysis of this material indicated that the sulfur content was 0.01% by weight or less. We utilized two methods of melting, as follows: e

(a) Arc melting in a water cooled copper crucible in an argon atmosphere to yield pancake shaped buttons weighing 250 grams; and

(b) Induction melting under vacuum in a refractory ceramic crucible to yield cast ingots of cylindrical shape, each weighing approximately 1000 grams.

Both types of ingot developed extensive intergranular fractures when we attempted to hammer forge them at 1100 C. Furthermore, our attempts to forge the arc melted ingots at 700 C. were likewise unsuccessful. Prior working of the ingots by a pressing technique also did not render them forgeable.

We then used the identical arc melting procedures to make melted buttons containing additions of the followingr I 0.4% Ce 0.1% Ce 1.0% mischmetal 0.4% mischmetal 0.2% mischmetal 0.2% Mn, 0.2% Ti, 0.2% Al In addition, various cobalt alloys shown in Table I were similarly prepared.

Although mischmetal is undoubtedly well known among those skilled in this particular art, for the sake of clarity, this is an alloy of rare earth metals containing about 50% cerium, the balance being lanthanum, neodymium and similar metals.

Following formation of the buttons, they were readily forged to bar stock.

The following table presents some of our data and illustrates the remarkably good results of our invention.

TABLE I Tensile properties of cobalt-base alloys Room Temperature 1,700 F.

Alloy (wt. percent) Reduov Reduc- UT tion in U'IS tion in (p.s.l Area (p.s.i.) Area (percent) (percent) C00.4 mischmetal 124, 000 28 16,100 20 Co0.5Zr ,500 83 138, 000 12 10,700 1 88 125,000 24 10, 700 32 158. 000 20 26, 72 163, 000 12 21, 500 88 127, 030 20 11, 600 44 140. 000 24 23, 300 32 127, 000 22 21, 000 82 177,000 17 26, 400 62 123,000 20 17,900 82 1 Specimens did not fracture. bioarm-Specimens tested as forged, treated 24 hr. at 1700 F. and air coo e It will be understood that modifications and variations may be effected without departing from the spirit and scope of the instant invention.

We claim as our invention:

1. A forgeable alloy consisting of from 0.1% to 0.4% cerium, the balance consisting essentially of cobalt.

2. A forgeable alloy consisting of from 0.2% to 1.0% mischmetal, the balance consisting essentially of cobalt.

3. A forgeable alloy consisting of from 1.0% to 5.0% niobium, the balance consisting essentially of cobalt.

,to 0.4% cerium, the balance consisting essentially of cobalt.

7. .A forgeable alloy consisting of 10.0% aluminum, 0.l%, ,to'0.4% cerium, the'balance consisting essentially of cobalt.

8. A f orgeable alloyconsisting offrom 2% to 10.0% tanta1um,. 0.l% to "0.4% ,cerium,'the balance consisting essentially of cobalt.

,9. A forgeablealloy consisting of an alloying material selected from the group consisting of the following in the stated amount byweight: cerium, 0.1% to 0.4%, mischmetal, ;2-% to 1.0%, niobium,=l% to 5%, and mixtures .tlierq bal q References Cited inthe'filc of -this patent UNITED STATES PATENTS Cooper Apr. 3, 1917 Franks et a1 Sept. 11, 1928 '4 2,046,995 Austin July 7, 19.36 2,126,749 De Golyer Aug. 16, 1938 2,133,291 Gordon Oct. 18, 1938 2,474,473 Ellis et al June 28, 1949 2,586,768 Bash Feb. 26, 1952 FOREIGN PATENTS 295,971 Great Britain Aug. 21, 1928 304,371 Great Britain 'J an. 21, 1929 488,963 Germany Jan. 13,1930

OTHER REFERENCES The Journal of the Institute of Metals, vol. XLIV (page 492 relied on). No. 2.

Breen et al.: Symposium on Metallic Materials for Service at Temperatures Above 1600 F., ASTM Special Technical Publication No. 174, 1956, pages 57-65.

Koster et al.: (I) Zeitschrift fiir Metallkunde, vol. 29, No. 7, July 1937, pages 230-231. Publishedvby Dr. Rieclerer Verlag G.m.b .H., Stuttgart, Germany.

Sykes: Transactions A.S.S.T., vol. 21, -1933,pages,4 16 .418. Published by the American Society for Metals, Cleveland, Ohio.

Koster et al.: (II) Zeitschrift fiir Metallkunde, vol. ;24, No. 12, December 1932, pages 296-298. 7

Koster et al.: (III) Zeitschrift fiir Metallkunde, Vol.56, No.3, March 1955, pages -197. 

2. A FORGEABLE ALLOY CONSISTING OF FROM 0.2% TO 1.0% MISCHMETAL, THE BALANCE CONSISTING ESSENTIALLY OF COBALT.
 3. A FORGEABLE ALLOY CONSISTING OF FROM 1.0% TO 5.0% NIOBIUM, THE BALANCE CONSISTING ESSENTIALLY OF COBALT.
 4. A FORGEABLE ALLOY CONSISTING OF 5.0% OF A METAL SELECTED FROM THE CLASS CONSISTING OF VANADIUM AND TUNGSTEN AND MIXTURES THEREOF, 0.1% TO 0.4% CERIUM, THE BALANCE CONSISTING ESSENTIALLY OF COBALT. 